A switching power supply is a power supply which maintains a stable output voltage by controlling a ratio of on-to-off time of a switch. Currently, switching power supply products are developing towards a direction of small type and high frequency, which results in difficulties in improvement of EMI noise in switching power supply products. A common mode inductor, as one of main components for suppressing EMI noise in a switching power supply, self characters of which have obvious influence on EMI noise suppression.
As shown in FIG. 1, an equivalent circuit diagram of a common mode inductor is illustrated. As shown in FIG. 2, a schematic structure diagram of a common mode inductor in conventional technologies is shown. The common mode inductor mainly includes a closed magnetic core 102 and two coil windings 101 symmetrically wrapped around the closed magnetic core 101. However, the EMI noise suppression capability of the common mode inductor still needs to be enhanced, which hampers the development of switching power supplies towards a direction of small type and high frequency.